The only problem with the 105mm lenses is their price. They just went through the roof on ebay. Some people ask for 300 Euros for a lens that cost less than that 20 years ago.
The 135mm lenses are a good choice, too. I own a 2.8 and two 3.5 lenses, and they are all excellent and do not cost much.
If you like zooms, the 4.5 /80-200 is a great lens, and it's often sold for next to nothing.